Oligo P-phenylenevinylene Research Articles

Tuning Sensing Efficacy of Oligo(phenylenevinylene) Based Chromogenic Probes: Effect of Alkyl Substituents on Metal Ion Detection at Micelle-Water Interface.

In this work, we conducted a comparative analysis of the metal ion sensing capabilities of two pyridine-end oligo p-phenylenevinylene compounds featuring different alkyl substituents (-C4H9 and -C16H33) within a micelle medium. Our findings revealed a correlation between the positioning of the probe molecules within the micelle and the length of the alkyl chains, impacting their self-assembly tendencies and optical characteristics. The compound with shorter alkyl chains demonstrated a superior affinity towards Hg2+ ions, whereas exposure to the compound with longer alkyl substituent resulted in a color-changing response with both Cu2+and Hg2+ ions. Intriguingly, the sensitivity towards Hg2+ ions heightened with increasing alkyl chain length. This trend persisted in non-polar solvents like THF. The capacity to modulate sensing efficacy solely by adjusting the length of the alkyl chains represents a relatively uncommon occurrence in the existing literature. This discovery suggests promising prospects for engineering sensory devices equipped with adaptable sensitivity.

Sequence-Specific Relay Recognition of Multiple Anions: An Interplay between Proton Donors and Acceptors.

Ratiometric detection of analyte is highly deserving since the technique is free from background correction. This work reports the design and synthesis of a pyridine-end oligo p-phenylenevinylene (OPV) derivative, 1 and its application in ratiometric dual-mode (both colorimetric and fluorogenic) recognition of dual anions, bisulfate (LOD=12.5 ppb) followed by fluoride (LOD=18.2 ppb) by sequence-specific relay (SPR) technique. The colorless probe turns brown with addition of bisulfate and again becomes colorless with the sequential addition of fluoride ion. In addition to such naked-eye color change, interestingly the ratiometric spectroscopic signals are reversible and evidently, the probe is reusable for several cycles. Besides, in presence of bisulfate, the protonated probe molecules, owing to their larger amphiphilic characteristics, formed self-assembled nanostructures. In addition to colorimetric and fluorescent changes, 1 H NMR titration and systematic DFT study evidently establish the underneath proton transfer mechanisms. Such reusable OPV-based chemosensor particularly with the capability of naked-eye recognition of dual anions using the SPR technique is seminal and possibly the first report in the literature.

Effects of different tailoring graphene electrodes on the rectification and negative differential resistance of molecular devices

The electronic transport properties of oligo p-phenylenevinylene (OPV) molecule sandwiched with symmetrical or asymmetric tailoring graphene nanoribbons (GNRs) electrodes are investigated by nonequilibrium Green’s function in combination with density functional theory. The results show that different tailored GNRs electrodes can modulate the current–voltage characteristic of molecular devices. The rectifying behavior can be observed with respect to electrodes, and the maximum rectification ratio can reach to 14.2 in the asymmetric AC–ZZ GNRs and ZZ–AC–ZZ GNRs electrodes system. In addition, the obvious negative differential resistance can be observed in the symmetrical AC-ZZ GNRs system.

Design of zinc porphyrin‐perylene diimide donor‐bridge‐acceptor chromophores for large second‐order nonlinear optical response: A theoretical exploration

AbstractThe electronic structures and second‐order nonlinear optical (NLO) properties of a series of zinc porphyrin (ZnP)‐perylene diimide (PDI) donor‐bridge‐acceptor (D‐π‐A) molecules have been investigated using density functional theory (DFT) and time‐dependent DFT (TDDFT). The results show that these compounds possess excellent second‐order NLO properties and large static first hyperpolarizabilities (β0) values on the order of 103 – 104 esu−30. A DFT benchmark calculation of β0 value was first performed, confirming the optimally tuned range‐separated functionals (LC‐BLYP* and ωB97X*) can produce similar magnitudes for β0 as Møller–Plesset second‐order perturbation (MP2) calculations. The magnitudes of β0 values were studied as a function of different types of bridges: oligo‐p‐phenylenevinylene (OPV), carbon‐bridged oligo‐p‐phenylenevinylene (COPV), oligo‐thienylenevinylene (OTV), carbon‐bridged oligo‐thienylenevinylene (COTV), and also the length of π‐bridges. The calculated β0 values were found to be inversely related to the bond length alternation (BLA) values of various π‐bridges. Next, we found that the static β0 value of designed ZnP‐COTV1‐PDI molecule can be significantly enhanced by finely tuning the dihedral angles between the π‐bridge and ZnP donor or PDI acceptor. The calculated β0 value is also sensitive to the substitution positions of PDI, that is, ortho‐(α‐), bay‐(β‐), nitrogen‐(N‐). A two‐level model was proven to be useful for the qualitative description of the β0 values and further the substantial oscillator strength and the difference in transition dipole moments between the ground and excited state mainly contribute to the large β0 values. The presented work will be beneficial for potential applications of the ZnP‐PDI‐based chromophores in the optoelectronic devices and high‐performance NLO materials.

Oligo p-Phenylenevinylene Derivatives as Electron Transfer Matrices for UV-MALDI.

Phenylenevinylene oligomers (PVs) have outstanding photophysical characteristics for applications in the growing field of organic electronics. Yet, PVs are also versatile molecules, the optical and physicochemical properties of which can be tuned by manipulation of their structure. We report the synthesis, photophysical, and MS characterization of eight PV derivatives with potential value as electron transfer (ET) matrices for UV-MALDI. UV-vis analysis show the presence of strong characteristic absorption bands in the UV region and molar absorptivities at 355 nm similar or higher than those of traditional proton (CHCA) and ET (DCTB) MALDI matrices. Most of the PVs exhibit non-radiative quantum yields (φ) above 0.5, indicating favorable thermal decay. Ionization potential values (IP) for PVs, calculated by the Electron Propagator Theory (EPT), range from 6.88 to 7.96 eV, making these oligomers good candidates as matrices for ET ionization. LDI analysis of PVs shows only the presence of radical cations (M+.) in positive ion mode and absence of clusters, adducts, or protonated species; in addition, M+. threshold energies for PVs are lower than for DCTB. We also tested the performance of four selected PVs as ET MALDI matrices for analytes ranging from porphyrins and phthalocyanines to polyaromatic compounds. Two of the four PVs show S/N enhancement of 1961% to 304% in comparison to LDI, and laser energy thresholds from 0.17 μJ to 0.47 μJ compared to 0.58 μJ for DCTB. The use of PV matrices also results in lower LODs (low fmol range) whereas LDI LODs range from pmol to nmol. Graphical Abstract ᅟ.

Impact of Vibrations and Electronic Coherence on Electron Transfer in Flat Molecular Wires

ABSTRACTElectron transfer in molecular wires are of fundamental importance for a range of optoelectronic applications. The impact of electronic coherence and ionic vibrations on transmittance are of great importance to determine the mechanisms, and subsequently the type of wires that are most promising for applications. In this work, we use the real-time formulation of time-dependent density functional theory to study electron transfer through oligo-p-phenylenevinylene (OPV) and the recently synthesized carbon bridged counterpart (COPV). A system prototypical of organic photovoltaics is setup by bridging a porphyrin-fullerene dyad, allowing a photo-excited electron to flow between the Zn-porphyrin (ZnP) chromophore and the C60 electron acceptor through the molecular wire. The excited state is described using the fully self-consistent ∆-SCF method. The state is then propagated in time using the real-time TD-DFT scheme, while describing ionic vibrations with classical nuclei. The charge transferred between porphyrin and C60 is calculated and correlated with the velocity autocorrelation functions of the ions. This provides a microscopic insight to vibrational and tunneling contributions to electron transport in linked porphyrin-fullerene dyads. We elaborate on important details in describing the excited state and trajectory sampling.

Remarkable Role of C-I···N Halogen Bonding in Thixotropic 'Halo'gel Formation.

Halogen-bonding-induced self-assembly in the solution of equimolar mixtures of certain pyridyl-ended oligo p-phenylenevinylene (OPV)-derivatives with 1,4-diiodotetrafluorobenzene is reported. The mode of self-assembly, that is, cocrystallization, thixotropic gelation, or precipitation, depends strongly on the nature of chains (n-alkyl chains as a function of length or short oxyethylene chain) appended to the OPV-backbone as well as on the cooling rate of the corresponding hot solution. Single-crystal X-ray diffraction studies of the cocrystals reveal the "infinite" chain formation via C-I···N halogen-bonding interactions between the two components. In addition, multiple noncovalent interactions induce cross-links among these halogen-bonded "infinite" chains. Interestingly, the molecular packing in the "Cogel" bearing OPV-derivative with oxyethylene chains is found to be very similar to that of the cocrystal of the same.

Tetramethoxybenzene is a Good Building Block for Molecular Wires: Insights from Photoinduced Electron Transfer.

Two donor bridge-acceptor molecules with terminal triarylamine and Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) redox partners were synthesized and investigated by cyclic voltammetry, optical absorption, luminescence, and transient absorption spectroscopy. The two dyads differ only by the central bridging unit, which was tetramethoxybenzene (tmb) in one case and unsubstituted phenylene (ph) in the other case. Photoirradiation of the Ru(bpy)3(2+) complex of the two dyads triggers intramolecular electron transfer from the triarylamine to the (3)MLCT-excited metal complex, and this process occurs with time constants of 1.5 and 6.8 ns for the tmb- and ph-bridged dyads, respectively. Thermal electron transfer in the reverse direction then leads to disappearance of the photoproduct with a time constant of 10 ns in both dyads. The faster rate of photoinduced charge transfer in the tmb-bridged dyad can be understood in the framework of a hole-tunneling model in which the electron-rich tmb bridge imposes a more shallow barrier than the less electron-rich ph spacer. Until now tmb-based molecular wires have received very little attention, and alkoxy substituents have been mostly used for improving the solubility of oligo-p-phenylene vinylene (OPV) and oligo-p-phenylene ethynylene (OPE) wires. Our study illustrates how four alkoxy-substituents on a phenylene backbone can have a significant influence on the charge-transfer properties of a molecular wire, and this is relevant in the greater context of a future molecular electronics technology.

Effects of amino-nitro side groups on electron device of oligo p-phenylenevinylene molecular between ZGNR electrodes

We study the electronic transport property for a molecular device of an oligo (p-phenylenevinylene) (OPV) molecule without or with different side groups between two zigzag-edged graphene nanoribbon (ZGNR) electrodes. By using ab initio calculations based on density-functional theory, the effects of negative differential resistance (NDR) and spin-rectifying in I–V characteristics are revealed and explained for the proposed molecular device. Our analysis indicates that the NDR behavior comes from the conduction orbital being suppressed under certain bias voltage, while the rectifying effect is because of the asymmetry distribution of the highest occupied molecular orbital or the lowest unoccupied molecular one as well as the corresponding coupling between the molecule and electrodes. Interestingly, the transport property of the device can be improved by introducing amino-nitro side groups to the OPV molecule. The NDR behavior can be much enhanced for molecule with amino side group, and the rectification can be improved for molecule with amino and nitro side groups, respectively. In particular, the NDR behavior of peak to valley ratio can be much enhanced and a molecular rectifier which offers rectification ratio of more than three orders of magnitude up to 2863 by adding NH2 and NO2 side groups to OPV molecule, respectively.

Synthesis and FET characteristics of phenylene-vinylene and anthracene-vinylene compounds containing cyano groups

A series of oligo-p-phenylene-vinylenes (OPVs) 1–3 and anthracene-vinylenes (AVs) 4–6 containing cyano groups have been synthesized and their photophysical, electrochemical and carrier transporting properties have been systematically examined. OPVs 2a and b, having cyano groups at the α-vinyl position, exhibited higher electron-accepting properties. Reduction peaks of OPV 2a in the cyclic voltammograms were observed as two-step reversible waves. OPVs 2a and b showed high electron mobilities in FET devices with bottom contact configuration. On the contrary, OPV 3a, which has cyano groups at the β-vinyl position, exhibited a high electron mobility of 0.3 cm2 V−1 s−1 with a top contact configuration. Introduction of biphenyl units enhanced the fluorescence efficiency in the solid state. In the case of AVs 5 and 6, cyano groups introduced at the 9 and 10-positions play an important role in injecting and transporting electrons. FET devices based on AVs 5 and 6 showed ambipolar behavior in the same device conditions.

Conjugation-length dependency of unsubstituted oligo- p-phenylenevinylenes on the performance of organic field-effect transistors

We have reported the conjugation-length dependency of unsubstituted oligo- p-phenylenevinylenes (OPVs) on the performance of organic field-effect transistors (OFETs). The experimental results have shown that the appropriate conjugation-length exists for obtaining high-performance OFETs with OPVs evaporated on the substrate at room temperature. It is considered that observed mobilities are determined by the hole injection barrier and the molecular orientation in the film. On the other hand, high-performance OFETs using OPV with a long conjugated length were obtained when the OPV was evaporated on the substrate at optimum temperatures. The OFET exhibited field-effect hole mobility up to 1.5 × 10 −1 cm 2 V −1 s −1.

Control of p- and n-type carriers by end-group substitution in oligo-p-phenylenevinylene-based organic field-effect transistors

Organic field-effect transistors (OFETs) consisting of vacuum-evaporated oligo-p-phenylenevinylene derivatives were prepared, and the device characteristics were evaluated. The fabricated OFETs showed typical p-type characteristics for methyl-substituted oligo-p-phenylenevinylene (OPV). A field-effect hole mobility of 0.13cm2V−1s−1 emerged with a threshold voltage of −33V and an on/off ratio of 5.8×105. On the other hand, OFETs showed typical n-type characteristics for trifluoromethyl-substituted OPV. A field-effect electron mobility of 0.013cm2V−1s−1 emerged with a threshold voltage of 45V and an on/off ratio of 4.2×104. The authors have observed clear changes from p-channel to n-channel conductions in OFETs by chemically modifying oligo-p-phenylenevinylenes.

Influence of mesoscopic ordering on the photoexcitation transfer dynamics in supramolecular assemblies of oligo- p-phenylenevinylene

We have investigated the influence of molecular arrangement on the transfer rates of photoexcitations along supramolecular assemblies of hydrogen-bonded oligo- p-phenylenevinylene (OPV) molecules for two different packing geometries. For well-defined, helical stacks of monofunctional OPVs fast (≈50 ps) photoluminescence depolarization and excitation transfer to dopants was observed, in agreement with semi-coherent exciton diffusion. For disordered assemblies of bifunctional OPVs incorporating a spacer to link adjacent molecules, depolarization and energy transfer dynamics occur on a longer time scale (≈nanosecond). This strongly suggests that such spacers need to be tuned carefully as they may otherwise interfere with the π-stacking thereby reducing the intermolecular electronic coupling.

The effects of supramolecular assembly on exciton decay rates in organic semiconductors

We present time-resolved photoluminescence measurements on two series of oligo-p-phenylenevinylene (OPV) materials that are functionalized with quadruple hydrogen-bonding groups. These form supramolecular assemblies with thermotropic reversibility. The morphology of the assemblies depends on the way that the oligomers are functionalized; monofunctionalized OPVs (MOPVs) form chiral, helical stacks while bifunctionalized OPVs (BOPVs) form less organized structures. These are therefore model systems to investigate the effects of supramolecular assembly, the effects of morphology, and the dependence of oligomer length on the radiative and nonradiative rates of pi-conjugated materials. The purpose of this work is to use MOPV and BOPV derivatives as model systems to study the effect of intermolecular interactions on the molecular photophysics by comparing optical properties in the dissolved phase and the supramolecular assemblies. A simple photophysical analysis allows us to extract the intrinsic radiative and nonradiative decay rates and to unravel the consequences of interchromophore coupling with unprecedented detail. We find that interchromophore coupling strongly reduces both radiative and intrinsic nonradiative rates and that the effect is more pronounced in short oligomers.

Resonance energy transfer dynamics in hydrogen-bonded oligo-p-phenylenevinylene nanostructures

Oligo-p-phenylenevinylene (OPV) materials monofunctionalised with ureido-s-triazine form chiral, helical stacks in dodecane solution. Here, we investigate resonance energy transfer dynamics in supramolecular stacks of OPVs consisting of three phenyl rings (MOPV3) doped with similar oligomers containing four phenyl rings (MOPV4). Broad spectral overlap between the MOPV3 fluorophores and MOPV4 chromophores results in efficient energy transfer from MOPV3 to MOPV4. We observe resonance energy transfer following two distinct regimes. The first is evident by growth of MOPV4 photoluminescence on a timescale of ∼50ps, mediated by rapid exciton diffusion in MOPV3 within the stack. In the second regime, dynamics of localised excitons on nanosecond timescales are dominated by direct resonance energy transfer to MOPV4 chromophores. Global analysis of the photoluminescence decay of MOPV3 in blends with varying MOPV4 composition on times ≳2ns is consistent with quasi-one-dimensional resonance energy transfer with Förster radius of 8nm.

Conformational gating of long distance electron transfer through wire-like bridges in donor-bridge-acceptor molecules.

A series of five donor-bridge-acceptor (DBA) molecules in which the donor is tetracene, the acceptor is pyromellitimide, and the bridge molecules are oligo-p-phenylenevinylenes (OPV) of increasing length has been shown to undergo electron transfer (ET) by means of two mechanisms. When the bridge is short, strongly distance dependent superexchange dynamics dominates, whereas when the bridge is longer, bridge-assisted hopping dynamics prevails. The latter mechanism results in relatively soft distance dependence for ET in which the OPV oligomers act effectively as molecular wires. We now report studies on the critical influence that bridge dynamics have on electron transfer through these oligomers. The temperature dependence of the charge separation (CS) rates in all five molecules does not appear to obey the predictions of standard ET theories based upon the Condon approximation. All five molecules show behavior consistent with CS being "gated" by torsional motion between the tetracene donor and the first bridge phenyl ring. This is based on the near equivalence of the CS activation energies measured for all five molecules with the frequency of a known vibrational mode in 5-phenyltetracene. In the molecule containing a trans-stilbene bridge, a competition occurs between the tetracene-phenyl torsional motion and one that occurs between the vinyl group and the phenyls linked to it. This results in complex temperature-dependent CS that exhibits both activated and negatively activated regimes. The charge recombination (CR) reactions within the molecules which have the two shortest bridges, namely phenyl and trans-stilbene, show a weaker dependence on these molecular motions. The three molecules with the longest bridges all display complex temperature dependencies in both their rates of CS and CR, most likely because of the complex torsional motions, which arise from the multiple phenyl-vinyl linkages. The data show that long-distance electron transfer and therefore wire-like behavior within conjugated bridge molecules depend critically on these low-frequency torsional motions. Molecular device designs that utilize such bridges will need to address these issues.

H- and J-aggregates of conjugated polymers and oligomers: A theoretical investigation

Excited-state interactions between two oligo-phenylene molecules are evaluated for different intermolecular orientations using singles configuration interaction with a Pariser–Parr–Pople Hamiltonian. As one molecule in a pair of cofacially overlapping molecules is displaced along its axis, an H- to J-aggregate crossover occurs at the slip fraction f 0. For intermolecular separations typical of polymer aggregates, f 0 initially decreases with oligomer size, but converges in the polymer limit to 0.44 and 0.48 for oligo- p-phenylene (OP) n and oligo- p-phenylene vinylene (OPV) n dimers, respectively. Relative intermolecular rotations are also investigated. Implications for larger aggregates are discussed.